Glandular Epithelium Function

Glandular epithelium consists of epithelial cells specialized in producing secretions. These secretions are released by a process known as exocytosis, not involving metabolic waste. The secreted products are stored in secretory granules—small, membrane-bound vesicles within the cells.

1.0Glandular Epithelial 

• Columnar and cuboidal cells often specialize into glandular cells, secreting enzymes, hormones, mucus, sweat, or saliva. Examples include salivary glands, sweat glands, and adrenal glands.
• Glandular cells derive substances from the blood and chemically modify them to form secretory products. These products are then discharged from the cell.

2.0Development of Glands

• Glands develop during fetal life by covering epithelia using cell proliferation and invasion of the subjacent connective tissue, followed by further differentiation, as shown in the following diagram.

3.0Type of secretion

Secretory epithelial cells may produce and release:

• Proteins – e.g., pancreas
• Lipids – e.g., adrenal and sebaceous glands
• Glycoproteins – e.g., salivary glands
• Combination of all three – e.g., mammary glands
• Water and ions – e.g., sweat glands (with minimal synthetic activity)

4.0Gland Categories

• Exocrine glands exude secretions into a ductule system. These glands have two parts: acinous = secretory bulb and ductule. 
• Endocrine glands are glands that exude secretions directly into blood vessels (capillaries), which transport blood to target cells throughout the body. 
• Mixed - glands combining both the above characteristics (e.g. liver) in the same cell 
• Paracrine - tissue secretions affecting own cells

5.0Cellular Composition

• Unicellular glands: Single cell, e.g., Goblet cells in GI and respiratory tract (mucus secretion)
• Multicellular glands: Multiple cells
• • Intraepithelial – found within epithelial layer
  • Extraepithelial – located in connective tissue (e.g., tubular or acinar glands)

6.0Modes of Secretion

1. Merocrine - secretion does not affect the well-being of the cell = sweat glands. 

2. Apocrine -  A small part of the cell cytoplasm is lost with the secretion; the cell is damaged but not killed, as in mammary glands. 

3. Holocrine - a lot of cytoplasm is lost with the secretion; the cell dies—sebaceous glands.

7.0Secretion Products

• Serous - thin, watery fluid, product of serous cells, small pink staining cuboidal cells with spherical to elliptical nuclei; salivary glands, sweat glands, pancreatic acinar.  
• Mucous - thicker, viscous secretion, product of mucous cells, large blue staining cuboidal cells with flat, elongated nuclei; GI tract, oral cavity.  
• Mixed serous-mucous - oral cavity, salivary.  
• Sebaceous - thick, lipid-rich secretions of cuboidal cells in certain skin regions - face, nose, axillary and pubic regions.

8.0Myoepithelium

• Myoepithelium - specialized squamous epithelial cells with powers of contraction;  Surround glandular acini and ducts of many glands, contain actin, myosin, cytokeratin = epithelial in origin, not muscle.

9.0Endocrine Glands

General Characteristics

• Ductless, release hormones directly into blood
• Rich in blood vessels and nerve fibers
• Each epithelial cell is closely associated with a blood capillary

Histological Types

• Trabecular – cells in cords (e.g., parathyroid, adrenal)
• Follicular – cells form follicles (e.g., thyroid)
• Disseminated – isolated cells or groups within organs (e.g., pancreas islets, Leydig cells)